It is a common practice to plug wells and to have encroachment of water into the wellbore above the plug. FIG. 1 illustrates this phenomenon. It shows a wellbore 10 through formations 12, 14 and 16 with a plug 18 in zone 16. Water 20 has infiltrated as indicated by arrows 22 and brought sand 24 with it. There is not enough formation pressure to get the water 20 to the surface. As a result, the sand 24 simply settles on the plug 18.
There are many techniques developed to remove debris from wellbores and a good survey article that reviews many of these procedures is SPE 113267 Published June 2008 by Li, Misselbrook and Seal entitled Sand Cleanout with Coiled Tubing: Choice of Process, Tools or Fluids? There are limits to which techniques can be used with low pressure formations. Techniques that involve pressurized fluid circulation present risk of fluid loss into a low pressure formation from simply the fluid column hydrostatic pressure that is created when the well is filled with fluid and circulated or jetted. The productivity of the formation can be adversely affected should such flow into the formation occur. As an alternative to liquid circulation, systems involving foam have been proposed with the idea being that the density of the foam is so low that fluid losses will not be an issue. Instead, the foam entrains the sand or debris and carries it to the surface without the creation of a hydrostatic head on the low pressure formation in the vicinity of the plug. The downside of this technique is the cost of the specialized foam equipment and the logistics of getting such equipment to the well site in remote locations.
Various techniques of capturing debris have been developed. Some involve chambers that have flapper type valves that allow liquid and sand to enter and then use gravity to allow the flapper to close trapping in the sand. The motive force can be a chamber under vacuum that is opened to the collection chamber downhole or the use of a reciprocating pump with a series of flapper type check valves. These systems can have operational issues with sand buildup on the seats for the flappers that keep them from sealing and as a result some of the captured sand simply escapes again. Some of these one shot systems that depend on a vacuum chamber to suck in water and sand into a containment chamber have been run in on wireline. Illustrative of some of these debris cleanup devices are U.S. Pat. No. 6,196,319 (wireline); U.S. Pat. No. 5,327,974 (tubing run); U.S. Pat. No. 5,318,128 (tubing run); U.S. Pat. No. 6,607,607 (coiled tubing); U.S. Pat. No. 4,671,359 (coiled tubing); U.S. Pat. No. 6,464,012 (wireline); U.S. Pat. No. 4,924,940 (rigid tubing) and U.S. Pat. No. 6,059,030 (rigid tubing).
The reciprocation debris collection systems also have the issue of a lack of continuous flow which promotes entrained sand to drop when flow is interrupted. Another issue with some tools for debris removal is a minimum diameter for these tools keeps them from being used in very small diameter wells. Proper positioning is also an issue. With tools that trap sand from flow entering at the lower end and run in on coiled tubing there is a possibility of forcing the lower end into the sand where the manner of kicking on the pump involves setting down weight such as in U.S. Pat. No. 6,059,030. On the other hand, especially with the one shot vacuum tools, being too high in the water and well above the sand line will result in minimal capture of sand.
What is needed is a debris removal tool that can be quickly deployed such as by slickline and can be made small enough to be useful in small diameter wells while at the same time using a debris removal technique that features effective capture of the sand and preferably a continuous fluid circulation while doing so. A modular design can help with carrying capacity in small wells and save trips to the surface to remove the captured sand. Other features that maintain fluid velocity to keep the sand entrained and further employ centrifugal force in aid of separating the sand from the circulating fluid are also potential features of the present invention. Those skilled in the art will have a better idea of the various aspects of the invention from a review of the detailed description of the preferred embodiment and the associated drawings, while recognizing that the full scope of the invention is determined by the appended claims.
One of the issues with introduction of bottom hole assemblies into a wellbore is how to advance the assembly when the well is deviated to the point where the force of gravity is insufficient to assure further progress downhole. Various types of propulsion devices have been devised but are either not suited for slickline application or not adapted to advance a bottom hole assembly through a deviated well. Some examples of such designs are U.S. Pat. Nos. 7,392,859; 7,325,606; 7,152,680; 7,121,343; 6,945,330; 6,189,621 and 6,397,946. US Publication 2009/0045975 shows a tractor that is driven on a slickline where the slickline itself has been advanced into a wellbore by the force of gravity from the weight of the bottom hole assembly.